Garen'shealth regeneration is greatly increased due to his passive, Perseverance. This only activates if he can avoid receiving champion or monster damage for 9 seconds, granting him exceptional sustainability in lane as minions do not stop this effect.
Garen'sDecisive Strike makes him a powerful chaser, easily closing the gap and silencing enemies before they can cast a slow or any debuff. It can also be used to make a swift escape since it removes slows.
This makes Garen very strong against most caster-type champions due to its silence; disrupting combos can save teammates by preventing casters (both AP and AD) from comfortably using all their skills before they endanger themselves, especially since Garen himself is naturally tanky enough to rush in with little casualties, be it 1 v 1 or in a large teamfight.
Decisive Strike can be used to return to/move between lanes quickly, as it has no mana costs and a fairly low cooldown, especially at higher ranks.
Decisive Strike resets Garen's auto-attack timer, effectively allowing him to deal good damage in a short period of time. However, Garen will have to come to melee range without a speed boost if he uses the skill to double-attack.
Garen can be lethal in early game fights, especially after getting his ultimate. Judgment deals good continuous damage to enemies and Decisive Strike's speed boost is good for chasing enemies. Demacian Justice also does extra damage based on how much health the enemy has missing
Garen's best starting skill is Decisive Strike, as it can be used to last-hit, silence, speed himself up, remove slows, reset autoattacks and has very high burst damage at early levels.
Courage and Decisive Strike mix well for a powerful chasing and escape combo. The speed boost from Decisive Strike allows you to get in or out of range, while the damage reduction of Courage allows you to mitigate any retaliation from enemies.
Unlike other abilities, Judgment remains active when Garen is stunned because it is not a channeled spell.
With some points into Judgment, Garen can easily farm and push minions with it.
Judgment is Garen's main source of damage, but has a significant cooldown and long duration to maximize its damage. Make sure you activate Judgment properly or you will be left being fairly ineffectual in combat while it is on cooldown.
Another option would be Youmuu's Ghostblade; it gives similar AD and Armor penetration, but it also gives critical chance and a short boost to movement and attack speed. This makes it a great late game item when critical chance outscales raw AD and Garen can use the extra attack speed to help destroy turrets.
They can also be built together for an easy source of 20% CDR to combine with Spirit Visage. This also increases wave minion clear due to minions having low armor values.
Last Whisper is a good counter to teams stacking mass amounts of armor but gives no defensive stats, which are important if you are to survive the enemy's damage long enough to deal yours.
Warmog's Armor can be a good choice as well; the item's passive along with Perseverance allows him to regenerate 0.6% of his health per second, allowing him to recover health quickly after teamfights without going back to base. The extra health along with Courage makes him very hard to kill in a teamfight.
In combination with Judgment, an early Sunfire Cape helps with Garen's wave clearing capabilities, as well as providing mixed damage and constant threat.
Garen damage output is very high early game; avoid early confrontations and play passively if needed.
Harass Garen in lane every few seconds, if possible, to minimize the effect of Perseverance.
Ranged champions can easily stop Perseverance with an auto-attack (unless Garen goes farther back, which forces him to miss last-hits) and farm in lane at a safe distance from him - they generally also have abilities to keep their distance. Ranged carries will scale stronger than him in this situation.
Avoid going into a brush that does not have a ward in it if Garen's current whereabouts are unknown. Garen players have a tendency to hide in bushes, due to the synergy between his silence from Decisive Strike and damage from Judgment.
Garen is a cooldown based champion. However, all of his ability cooldowns are high. Try to attack him when they are on cooldown.
Decisive Strike is very good at stopping combos due to its silence; if you happen to be playing a caster champion who relies a lot on their abilities to deal most of their damage, be wary of this ability as Garen can save a teammate or even himself from your burst, as well as leaving you without the use of your defensive abilities or summoners such as Flash.
It is often worth the investment to purchase armor to counter Garen's high physical damage.
Think carefully before using your Crowd Control abilities on Garen. His Decisive Strike will remove Slows and Courage will reduce the duration of such abilities by 30% while active. Additionally, hard CC will not stop Judgment, only his movement. Keep away from him, especially if playing squishier champions as it deals very high damage over a short duration.
Like most melee champions, Garen is quite vulnerable to ranged harassment.
However, because of his high damage and better durability, he can force ranged champions away or even kill them if he gets all his damage off.
Buying a Hexdrinker may help as it can block a fair amount of damage from Garen'sDemacian Justice early on. Do not forget that his main form of damage is still physical, however.
Teemo is considered to be one of the best known counters to Garen. He can effectively poke and escape from him, if played correctly. Teemo'sBlinding Dart can be used to both deal damage and prevent him from dealing damage with Decisive Strike (the silence will still affect you). Toxic Shot allows you to harass and prevent his Perseverance from activating, and Noxious Trap allows you to slow and zone him. Use it while you are escaping from him, then retaliate when he attempts to escape. Keep in mind, however, that his combo is strong enough to kill you at early levels and he can utilize the brush to prevent you from harassing him.